1. Field of the Invention
The invention relates to the detection of dial pulses for a telephone communication switching system, and more particularly to detect only legitimate dial pulses and convert them into logic signals for use in the registers of a communication system.
2. Description of the Prior Art
The invention was developed for the system shown in U.S. Pat. No. 3,767,863, issued Oct. 23, 1973, by Borbas et al. for a Communication Switching System with Modular Organization and Bus, hereinafter referred to as the System S2 patent.
The previous system is described in U.S. Pat. No. 3,487,173, issued Dec. 30, 1969, by Duthie et al. for a Small Exchange Stored Program Switching System, hereinafter referred to as the System S1 patent. The dial pulse receiver of the S1 System was disclosed in U.S. Pat. No. 3,678,197, issued July 18, 1972 by Panter et al. for a Dial Pulse Incoming Trunk and Register Arrangement.
The dial pulse receiver (designated Dial Pulse Corrector, FIG. 11) in the Panter et al. patent was a discrete component circuit. This circuit has four transistor circuits and two capacitors. Two transistors served as in/out transistors and were coupled to the make and break contacts of a C contact (make and break contact) pulsing relay. The two capacitors and the four transistors provided the necessary delay by discharging or charging the respective capacitors. The accuracy of this circuit was, of course, dependent upon the various discrete components in the circuit and would vary from circuit to circuit by the nature of the components comprising the circuits. The number of discrete components in this circuit also made it an expensive circuit in comparison to the chip logic that was available for utilization in the System S2. This circuit could also not be adapted to the System S2 requirements as the battery feed device (BFD) in System S2 has only an A contact (make only contact).